This invention concerns a process for producing a tubular rubber product such as rubber hose, rubber coupling and the like laminated with a synthetic resin layer and, more specifically, it relates to a process for producing a tubular rubber product having a polyamide resin and/or polyester resin layer laminated thereon as a synthetic resin layer.
The surface of rubber is not always sufficiently resistant to chemicals such as organic solvents and, accordingly, with an aim of improving the organic solvent-resistance of rubber, various methods have hitherto been employed including, for instance, (1) use of rubber material with the different polarity from that of the solvents, (2) increasing in the cross-linking rate of rubber, (3) increasing the amount of filler and (4) increasing the amount and the thickness of the rubber employed.
However, these methods suffer from the following drawbacks respectively. Specifically, the method (1) requires expensive rubber such as chloroprene rubber (CR), butadiene-acrylonitrile rubber (NBR), acrylic rubber, epichlorohydrin rubber and fluorine rubber. The method (2) results in a problem of impairing the flexibility or the flexion resistance of rubber and the effect itself on improving the organic solvent-resistance is not so excellent. The method (3) has an upper limit for the filler amount in view of the workability and the physical properties of the rubber and it can provide an improving effect for the organic solvent resistance only in proportion to the volume fraction of the filler. Furthermore, the method (4) has a problem in that increasing in the thickness causes an increase in the weight of the product which results in the cost increasing and impairing the flexibility of the product.
In addition, the rubber material has a low resistance to gas permeation. As compared with 6-nylon, the permeation resistance to O.sub.2 and N.sub.2 is about 1/30-40 for isobutylene isoprene copolymer rubber (IIR) which is considered to have the most desirable permeation resistance among various rubbers and are as low as about 1/500-1/600 for butadiene rubber (BR).
Furthermore, another problem is that the rubber material is blended with various chemicals such as aging stabilizers, vulcanizers, vulcanization promotors and oils, and they are partially leached out of rubber material under certain conditions which circumstances and deteriorates the rubber properties.
In addition, since the surface of rubber has a large frictional coefficient, its results in a large flow resistance to a fluid flowing thereover. Undesirable pressure loss occurs while the fluid moves through the inside of tubular rubber products. Therefore, it is desired to reduce friction on the rubber surface in order to overcome the foregoing problem.
The various problems involved in the rubber material as described above, also occur in tubular rubbery products such as rubber hoses, rubber couplings and the like.
Rubber hoses have a wide variety of uses such as for automobile fuels, air conditioners, refrigerators, propane gases, hydraulics, as well as domestic uses, and various fluid medium are passed through the hoses such as organic solvents or gases as well as water and oils. Thus, although it is desirable for the rubber hoses to have acceptable low resistance to the fluid mediums, high flexibility, excellent low temperature properties, as well as being excellent in the matching performance with metal caps and inexpensive in cost, conventional rubber hoses do not always satisfy the aforegoing requirements.